The present invention relates to the field of downhole packers. More particularly, the present invention relates to an expandable packer for obstructing a space between downhole well components or between well tubing and a wellbore casing or open wellbore surface.
Downhole packers seal the annulus between well tubing and the wellbore, and between well tubing and casing set in the wellbore. By sealing such annulus, hydrocarbon producing zones can be isolated from other regions within a wellbore, thereby preventing migration of fluid or pressure between zones.
Packers typically comprise permanent or retrievable packers. Permanent packers are installed in the wellbore with mechanical compression setting tools, fluid pressure devices, inflatable charges, or with cement or other materials pumped into an inflatable seal element. Because of the difficulty of removing permanent packers, retrievable packers have been developed to permit the deployment and retrieval of the packer from a particular wellbore location.
Conventional packers typically comprise a sealing element between upper and lower retaining rings or elements. U.S. Pat. No. 4,753,444 to Jackson et al. (1988) disclosed a packer having a conventional sealing element located around the outside of a mandrel. Anti-extrusion rings and back-up rings contained the seal element ends and were compressed to radially expand the seal element outwardly into contact with the well casing. U.S. Pat. No. 4,852,649 to Young (1989) disclosed packers having multiple moving packer elements which distributed stresses across the elements as the packer elements expanded to seal the wellbore annulus. In U.S. Pat. No. 5,046,557 to Manderscheid (1991), multiple seal elements were separated with spacers around the exterior surface of a mandrel. The seal elements were hydraulically set to contact the well casing.
Other concepts have been developed for specific seal requirements. In U.S. Pat. No. 5,096,209 to Ross (1992), voids were incorporated within sealing elements to modify the performance of the seal elements in the sealing gaps between multiple tubing elements. In U.S. Pat. No. 5,195,583 to Toon et al. (1993), bentonite was placed within a packer element so that contact with water caused seal element expansion to form a low pressure annular seal.
U.S. Pat. No. 5,467,822 to Zwart (1995) disclosed a fluid pressure set pack-off tool wherein a seal element was retained with rings and annular inserts. Coaxial springs reduced distortion of the seal element and facilitated retraction of the seal element following removable of the fluid pressure. Radial bores through the seal element prevented entrained air from distorting the seal element and further permitted a higher pressure to press the seal element into sealing engagement with the well casing.
One limitation of conventional packers is that the exterior sealing element travels on the packer exterior from the well surface to the downhole location. When the packer is run thousands of meters into the wellbore, the packing seal can abrade or completely swab off the packer sleeve. This failure may not be detected until the packer is set and the pressure containment of the isolated zone fails.
Another limitation of conventional packers is the requirement for packers having high expansion capabilities. High expansion packers are often required below tubing and other restrictions in a wellbore to isolate lower production or well treatment zones. If a tubing string is established in a wellbore with a primary packer to seal the annulus between the wellbore and the tubing exterior surface, an additional packer may be run through the tubing interior space to a wellbore location downhole of the primary packer. If the additional packer is located past the tubing string end, such packer must expand from the thin through-tubing dimension to fill the larger wellbore annulus.
To accomplish high expansion capabilities, conventional inflatable packers have been modified to meet the expandability requirements. Inflatable packers having expandible back-up rings have been created to provide high expansion capabilities for such applications, such as U.S. Pat. No. 3,706,342 to Woolley (1972). In Woolley, the sealing element was positioned about a central tube, and was expanded with overlapping finger elements. Such conventional compression style seal elements are constrained by complex anti-extrusion backup systems, extreme buckling of the sealing element, and excessively long setting strokes.
Accordingly, a need exists for a high expansion packer that avoids the disadvantages of conventional packers and provides a reliable seal between different components and features downhole in a wellbore.